A. Field of the Invention
The field of the present invention relates generally to positioning devices utilized to precisely position a work tool, such as a drilling or milling machine, above a workpiece. More specifically, this invention relates to such devices that utilize a visual mechanism to locate the precise center, specific spot or edge of the workpiece so that such position may be used as a reference point for performing work operations. Even more specifically, this invention relates to such devices that utilize a light beam, such as from a laser, as the visual mechanism.
B. Background
When working a piece of material with a milling machine or similar type of work tool, the machinist must first identify a reference or starting point from which the various dimensions and locations for the milling work to be performed on the workpiece will be measured. As known by those skilled in the art, failure to properly identify the reference point will generally result in a waste of time and material as the milling work is improperly positioned on the workpiece. Once found, this reference or starting point on the workpiece is then set in corresponding relationship with the centerline of the working part of the milling machine or other work tool so that the milling work will be performed at the correct location. The most common reference point utilized by most machinists is either the center or an edge of the workpiece. From the center or edge of the workpiece, dimensions are utilized to properly position the workpiece under the milling machine so that the work operation is performed at the desired location. Typically, the workpiece is generally clamped or otherwise held in place on a table under the working part of the milling machine. For the center of the workpiece, the machinist will typically first manually measure, locate and then mark the center with a punch. Once the center or edge of the workpiece is found with respect to the centerline of the milling tool, which typically requires some adjustments, the machinist can perform the desired operations at the correct location. A similar type of process can also be used for identifying the position of holes, which may need to be drilled, tapped, edges chamfered, countersunk or have other work done, to be drilled into or through the workpiece. Once the hole locations are identified by prick-punching the workpiece, the ability to accurately drill at the hole position is somewhat based on the machinist's ability to position the workpiece with regard to the centerline of the drill press spindle.
The procedures and tools utilized by most machinists to locate the center or edge of a workpiece relative to a milling machine or other work tool indirectly locate the reference point, in that they require the machinist to make measurement adjustments. A common method utilized to find an edge of a workpiece is generally referred to as the contact or bump method. In this method, a simple piece of round stock is placed in the mill spindle and the work tool is hand cranked to gently abut the edge of the workpiece against the round stock. To align the work machine with the edge of the workpiece, the machinist then raises the round stock above the workpiece and moves the workpiece over half the diameter of the round stock. The micrometer dial setting at this position is zeroed to correspond to the edge of the workpiece, thereby aligning the work tool (i.e., the spindle centerline) with the plane running through the edge of the workpiece. Although the contact or bump method is quick and simple, it is well known that it is generally not that accurate due to the inherent problems associated with trying to recognize when the contact occurs and the elasticity of the materials involved. In addition, to the inherent accuracy problems, it is not that uncommon for machinists, particularly relatively inexperienced or hurried machinists, to forget to take into account the one-half of the diameter of the round stock used as the edge finder. Another problem known to be associated with this method of edge finding is that too much contact against the workpiece, which for certain metals is not that much contact, can dent or otherwise damage the workpiece.
Another method for finding the edge of a workpiece utilizes a tool commonly known as a wiggler, which has been used by machinist for over a century. Most wiggler sets come with an edge finder component that has a generally mushroom-shaped disk contact at the end of the wiggle shank opposite that which fits into the collet, typically in a ball and socket type of arrangement. As with the contact method described above, the workpiece is moved towards the spinning edge finder until it gently touches the disk contact and steadies the wiggling. The workpiece is then slowly dialed further towards the edge finder until it is spinning true (i.e., no wiggle). At the point the edge finder starts to slip sideways from the drag of the spinning disk against the workpiece, the machinist has found the edge of the workpiece. As with the contact method, the machinist then raises the edge finder and dials in half of its diameter, typically 0.100 inches, to align the spindle centerline with the edge plane of the workpiece. Although the wiggler edge finder is generally considered to be very accurate for routine machine work and good enough for most high precision work, it is known to be frustrating to utilize due to the fact that it has to be reset for each edge contact.
The typical wiggler set also includes a pointer component that fits within the same wiggle shank, but has a pointed end instead of the mushroom-shaped disk contact for the edge finder component. When the wiggle shank is chucked into the milling machine or other work tool and run, the end of the pointer will spin in a random-angled cone. The machinist, typically utilizing his or her thumbnails or other parts of their fingers, will guide the end to concentricity to correspond with the work tool spindle axis. The machinist then guides the workpiece to position the center punch mark, using visual alignment, under the pointed end to align the mark with the spindle axis. Unfortunately, manually adjusting the wiggler point to concentricity can result in injury to the machinist's finger(s), particularly for the novice machinist. If the wiggler is guided past center, the pointed end has a tendency to wildly spin, requiring realignment. Although this method can be very accurate, it does require the machinist to eyeball the alignment by mentally projecting a straight line to the marked center point of the workpiece.
Another well known mechanical edge finder utilizes a spring loaded conical disc that spins while free of the workpiece and then suddenly kicks or slips sideways when contact with the edge of the workpiece is obtained. Unlike the wiggler edge finder, however, the disc of this type of edge finder only slips a certain amount and then goes no further. As a result, the machinist can back up and try again without having to reset the contact by hand. Once the edge is found, the machinist moves the workpiece, generally by moving the mill table, over one-half the diameter of the edge finder to align the spindle axis with the plane of the workpiece edge. Some of these types of edge finders include a conically-shaped center finder having a pointed end that is utilized in the same manner as that described above for the wiggler center finder component.
A number of prior art center and/or edge finders are described in issued patents. For instance, U.S. Pat. No. 3,999,299 to Johnson describes an edge finder having a housing adapted to be received by the chuck on a work tool spindle, a slide biased against the housing by a spring that permits lateral movement of the slide and an outwardly extending finger that is rotatably attached to the slide at one end and shaped with a flat face at the other end to engage the side or edge of the workpiece. The plane of the flat face is configured to be in alignment with the axis of the work tool. Like the prior art devices set forth above, the workpiece is moved towards the edge finder until the edge is brought into contact with the flat face, at which time the slide moves at a right angle to the direction the workpiece is traveling indicating alignment with the edge. Unlike the above devices, however, no measurement adjustment is required. U.S. Pat. No. 5,217,336 to LeBlanc discloses an edge finder having an elongated body with a push pin at the semi-circular cross-section lower end that is contacted by the edge of the workpiece to operatively engage a lever connected to a dial indicator. The plane of the flat side of the lower end, which comes into contact with the workpiece edge when the pin is fully engaged, is in alignment with the axis of the spindle, thereby eliminating the need to factor in an adjustment. U.S. Pat. No. 4,429,463 to Angell discloses an electro-mechanical datum point locator tool that utilizes a cylindrical tip assembly that has an electrically conductive sleeve which causes a light to be emitted from the circumference of the tool's cylindrical housing when contact with the edge of the workpiece is obtained. The machinist must adjust for one-half the diameter of the tool's tip. U.S. Pat. No. 5,276,975 to Fisher describes an audible-visual edge finder having a working end member at the end of a cylindrical shank. The working end member has a flat that is configured to make an audible sound when it contacts the workpiece and to cause the finder to vibrate radially, thereby enhancing the sideways jump, to visually signal contact with the workpiece. Like the above patent, the machinist must adjust for one-half the diameter of the working end member. U.S. Pat. No. 4,622,751 to Berg describes an electromechanical measuring device having a workpiece contacting finger connected to a strain gauge or pressure transducer to locate the center of circular bores and pins relative to the axis of rotation of the spindle.
While the forgoing prior art devices and patents describe center and/or edge finders that are configured to locate and position the axis of the spindle above the center or edge of a workpiece, they all have limitations that either reduce their accuracy or effectiveness. For instance, the devices that require the machinist to add one-half the width or diameter of the tool are indirect methods of finding the workpiece edge or center, which can be forgotten by the novice or rushed machinist. Naturally, this mistake generally results in a waste of time and material. All of the aforementioned devices require the machinist to push the workpiece into contact with the edge finder in order to locate the edge of the workpiece, a process that always presents the potential of damaging the workpiece or precision tool if too much force is applied. A number of the aforementioned devices are not configured or useful for finding the center of a workpiece. What is needed, therefore, is a workpiece center and edge finder that provides direct indication of placement of the spindle axis over the edge or center of the workpiece without requiring physical contact between the workpiece and the finder tool. The preferred center and edge finder should be adaptable to a wide variety of work tools, including milling machines, lathes and the like. The preferred center and edge finder should be relatively simple to use.